Whats up with LCD prices?

My search for an LCD has taken me all over. Checked Apollo, Earth and so on but $350 to $500 for a bare 5.7" module seems expensive to me. Due to my in dash install requirments I can't use one of those pre-built self enclosed units. Not sure how they compare in brightness and so on but still they are far less expensive then the modules I priced. Some even come with built in speakers and mutiple mounting brackets for around $200. Assuming the specs were good is there any reason why you could not pull one of these apart and just use the Module?

I believe most of the price difference is in the interface. Most of the screens you see for cheap are a simple RCA input. All or most of the screens on EarthLCd and others are going to be VGA and prolly higher brightness.